For quite some time those in the art have been searching for a film material which, if apertured, has the ability to self seal and close the apertures in the presence of water vapor. Such a film would have considerable usefulness in a wide variety of areas. An exemplary area of application of such a material would be in the formation of tent fabric. If the fabric was slightly apertured, a film which would self seal in response to contact with water or water vapor would be highly desirable.
During experimentation directed to measuring the water vapor transmission rate (WVTR) of various apertured film materials we observed that certain commercially available trash bags, when apertured, self sealed during the WVTR test. We hypothesized that this action was due to the presence of an additive or additives to the film which was not normally present in polyethylene trash bags. Possible components of this sort were starch and iron oxide. We were able to check the possibility of whether starch, by itself, was the self sealing factor by testing commercially available film containing starch as an additive but not iron. As aperture closure did not occur, we concluded that starch, by itself, did not appear to be the component causing the observed result. Plastic film containing only iron oxide as an additive is not known to us to be commercially available. However, it is known that, under certain conditions, Fe.sub.2 O.sub.3 in the presence of water will form a hydroxide Fe(OH).sub.3 which is a sol. This material by itself or in the presence of starch would flocculate and explain the observed aperture sealing. It should be noted that other metal hydroxides exhibit similar behavior to iron. Accordingly, we set out to determine if a self sealing film could be formed from a polymer system containing a small amount of a gelling/swelling agent as a simpler method of achieving the results observed with the iron starch system.
Prior documents in this area include U.S. Pat. No. 4,913,517 to Arroyo et al., U.S. Pat. No. 3,890,974 to Kozak, Canadian patent application number 2,005,764 to Bottiglione et al., European patent application number 0 378 940 A1, Kolloid Zeitschrift V-74, pp. 200-205 (1936) and The Principles of Colloid and Surface Chemistry, second edition, by P. C. Hiemenz, pp 782-783 (1986).